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Digital Signal Processing Techniques for the GIFTS SM EDUThe Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) Sensor Module (SM) Engineering Demonstration Unit (EDU) is a high resolution spectral imager designed to measure infrared (IR) radiance using a Fourier transform spectrometer (FTS). The GIFTS instrument employs three Focal Plane Arrays (FPAs), which gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral bands. The raw interferogram measurements are radiometrically and spectrally calibrated to produce radiance spectra, which are further processed to obtain atmospheric profiles via retrieval algorithms. This paper describes several digital signal processing (DSP) techniques involved in the development of the calibration model. In the first stage, the measured raw interferograms must undergo a series of processing steps that include filtering, decimation, and detector nonlinearity correction. The digital filtering is achieved by employing a linear-phase even-length FIR complex filter that is designed based on the optimum equiripple criteria. Next, the detector nonlinearity effect is compensated for using a set of pre-determined detector response characteristics. In the next stage, a phase correction algorithm is applied to the decimated interferograms. This is accomplished by first estimating the phase function from the spectral phase response of the windowed interferogram, and then correcting the entire interferogram based on the estimated phase function. In the calibration stage, we first compute the spectral responsivity based on the previous results and the ideal Planck blackbody spectra at the given temperatures, from which, the calibrated ambient blackbody (ABB), hot blackbody (HBB), and scene spectra can be obtained. In the post-calibration stage, we estimate the Noise Equivalent Spectral Radiance (NESR) from the calibrated ABB and HBB spectra. The NESR is generally considered as a measure of the instrument noise performance, and can be estimated as the standard deviation of calibrated radiance spectra from multiple scans. To obtain an estimate of the FPA performance, we developed an efficient method of generating pixel performance assessments. In addition, a random pixel selection scheme is developed based on the pixel performance evaluation. This would allow us to perform the calibration procedures on a random pixel population that is a good statistical representation of the entire FPA. The design and implementation of each individual component will be discussed in details.
Document ID
20070032919
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Tian, Jialin
(Science Systems and Applications, Inc. Hampton, VA, United States)
Reisse, Robert A.
(NASA Langley Research Center Hampton, VA, United States)
Gazarik, Michael J.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 23, 2013
Publication Date
January 1, 2007
Subject Category
Earth Resources And Remote Sensing
Meeting Information
Meeting: 2007 AMOS: 8th Annual Advanced Maui Optical and Space Surveillance Technologies Conference
Location: Maui, HI
Country: United States
Start Date: September 12, 2007
End Date: September 15, 2007
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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